Some conventional image forming apparatuses, in order to judge whether a waste toner container is loaded, detect weight of the waste toner container loaded in the loading place.
Some other conventional image forming apparatuses employ a drive torque for judging whether a waste toner container is full of waste toner. The drive torque, provided to transporting means for transporting used toner, detects the full waste toner container when amount of transported waste toner exceeds a predetermined value. An image forming apparatus of this type is disclosed in Japanese Laid-Open Patent Publication No. 4-106577/1992 (Tokukaihei 4-106577).
Some other conventional image forming apparatuses employ a shutter for preventing transported waste toner from falling into a waste toner collecting device when no waste toner container is loaded. The shutter, provided at the end of a toner transporting pipe close to the waste toner container, is closed when no waste toner container is loaded. An image forming apparatus of this type is disclosed in Japanese Laid-Open Patent Publication No. 58-31368/1983 (Tokukaishou 58-31368).
There are problems with the conventional image forming apparatus detecting the weight in order to judge whether the waste toner container is loaded. For example, when there is something of the same weight as the waste toner container in the loading place for some reason, the apparatus makes a misjudgement that the waste toner container is loaded, the misjudgement leading to a faulty operation. Besides, since the weight of the waste toner container varies depending on amount of the waste toner collected in the waste toner container, a complex and costly structure is needed for higher accuracy in the weight detection process. Also, there are problems with the conventional image forming apparatus which only judges whether the waste toner container is full of waste toner. For example, a separate detecting system is needed for judging whether the waste toner container is loaded in the loading place, and this makes the image forming apparatus more complex and costly. Also, there are problems with the conventional image forming apparatus employing the shutter. For example, since the shutter can only prevent transported waste toner from falling into the waste toner collecting device when no waste toner container is loaded, the shutter cannot stop the waste toner transportation itself. Therefore, the shutter cannot completely solve the problem that the waste toner is transported to the unloaded waste toner collecting device, and makes the image forming apparatus more complex and costly.
To sum up the above discussion, the conventional image forming apparatuses have common problems of faulty operation, a complex structure and a high cost.